How to Comply with Part 135 Air Ambulance Obstacle Requirement Using ForeFlight

You may be familiar with some of the regulations governing how FAA Part 135 aircraft operators prepare for and conduct flights, but did you know that helicopter air ambulance operators have a number of special rules all to themselves under Part 135? One of these requires the pilot of any VFR flight to identify and document the highest obstacle along the planned route (§135.615). This ensures that the pilot briefs this potential hazard and determines the minimum safe altitude for the flight.

While a good safety measure to prevent collisions, the requirement has been a pain point for some operators as the somewhat vague guidance to “identify and document” is left open to interpretation. Not to mention that some methods of complying with the requirement could take up a good chunk of a pilot’s preflight preparation time, which is at a premium with air ambulance operations.

Fortunately for air ambulance operators using ForeFlight, there is a fast and easy method of complying with the highest obstacle requirement in the app itself. This method employs ForeFlight’s Profile view (available with Pro and Pro Plus subscriptions).

Viewing obstacles along your route using Profile view

Start by entering departure and destination points in the Route Editor, then tap Profile to view the vertical cross-section of the planned route.

Terrain and obstacles are dynamically highlighted based on relative height to your selected altitude. Tap and hold anywhere in the Profile window (other than directly under the altitude box) and a vertical dotted line and box will appear showing that point’s altitude in MSL, the clearance in feet between the point and your planned altitude, and the distance of that point from your departure point. Dragging your finger right or left shows this information for any point along your route. The selected point is also displayed on the “top-down” view of your route below, revealing where the point is along your route.

Use Profile view to measure and document the highest obstacle along your route.

The profile window also allows for pinch-zooming and dragging so you can unclutter nearby obstacles. You can change the total width of the corridor shown in Profile by tapping the button at the bottom-right of the window and tapping “Corridor Width” at the bottom of the popup.

Using Profile view allows the highest obstacle along a route to be easily identified. As for “documenting” it, simply place the dotted line on the highest point and take a screenshot by pressing the iPad’s home and lock buttons at the same. The screenshot can then be accessed and shared from the iPad’s Photos app, or from a cloud storage app like Dropbox.

A number of air ambulance operators using ForeFlight have shared with us how this feature helps them comply with the highest obstacle requirement. We hope this helps you, too.

All FBOs Check-in with ForeFlight at 2016 NBAA S&D Conference

Team ForeFlight will be on hand at the 2016 NBAA Schedulers & Dispatchers Conference this week—stop by and visit with Jamie and Linda in Booth #100. Products on demonstration include ForeFlight’s FBO Directory, ForeFlight Web (our web-based flight planning platform), and JetFuelX (a planning tool that helps operators manage contract fuel memberships).

ForeFlight FBOs on Taxi Charts

More than 2700 FBO locations are mapped on ForeFlight Taxi Charts. Featured listings are highlighted in yellow and pilots can access listing details right from the taxi chart view.

Corporate, fractional, and charter operators use ForeFlight everyday for fuel stop and destination planning, and they are thrilled with our new FBOs on Taxi Charts feature. FBOs on Taxi Charts allow pilots to see exactly where your business is located on the field and to access FBO Directory listings right from the taxi chart view.

As an FBO, you have the opportunity to enhance your listing in the most widely used aviation app so that your business stands out above the rest. At the exhibit, we can show you a live demo of what your business listing looks like and what our customers see in real-time. In addition, check out this article from Linda Street-Ely, our ForeFlight Directory Manager, for pro tips on the features of Directory.

We also recently announced the acquisition of JetFuelX—a free web–based fuel card management service that makes it easy for owners and operators of turbine aircraft to save money by quickly finding the lowest prices available from their multiple jet fuel discount program memberships. FBOs and fuel providers benefit, too, as you can build your fuel discount program membership and efficiently distribute pricing data to customers. If you are interested in integrating your fuel discount program, contact info@jetfuelx.com to learn more.

See you in Tampa!

How To Find Valuable Planning Info in ForeFlight’s FBO Directory

As ForeFlight Directory Manager, I communicate daily with FBOs and other businesses of interest to pilots. I love to help businesses get the most out of their presence in the ForeFlight Business Directory, and to help ForeFlight subscribers know where to find that information. Here are some Pro Tips on ForeFlight Directory features that everyone can use:

Finding Fuel Prices
Fuel prices can be viewed as an interactive Map layer as well as within an FBO directory listing.

ForeFlight Directory listing on maps view.

ForeFlight Directory List view shown on the Maps view. Turn on the “Fuel: 100LL” layer and tap on a marker to view FBO details.

The price that is shown on the Fuel: 100LL layer in the Maps view and on the FBO List view (found by tapping the FBOs button in the Airport view or by tapping on a marker in the Maps view) is a summary of the lowest price options. An FBO that sells both full-service and self-serve 100LL will likely have two different prices. Tap on the business listing to reveal more information and ensure you are viewing all available 100LL fuel prices.

ForeFlight Directory detail view on Maps layer

In this example, tap directly on the ACI Jet listing to reveal more FBO details and all available retail fuel prices they offer.

We actively partner with FBOs to help them keep their listing information and fuel prices up-to-date. However, if you find the price you pay at the pump is different from our last update, you can help update the price right through the app. To submit fuel price updates, from the Airport view, tap FBOs, then tap on the FBO of choice. On the lower right corner, tap Update Fuel Prices. Enter the current price and tap Submit.

The ACI Jet detail view is shown here in the Airports view. The airport Comment and FBOs buttons are highlighted in the upper right. The Add Comment and Update Fuel Prices buttons specifically for ACI Jet are highlighted at the bottom of the listing window.

Many businesses add a custom description, tappable links to their website and social media, photos, affiliate service badges, and company logo. The Business Directory is rich with data and images to help pilots and trip planners make more informed decisions.

Sharing Your Experience With Comments
ForeFlight customers can submit two kinds of comments: feedback on the airport in general and feedback on the specific business they visited.

We hope you have a great experience to share with fellow pilots, however if there is an issue we encourage you to contact the FBO or other business directly first to resolve the situation. Comments are published unedited (with the exception of gate codes and special fuel prices) and identify you as the commenter using the part of your email address that is before the “@” sign.

Airport Comments buttonNotice there are two areas within the Airport Comments section: Remarks and Comments. Remarks are official Airport Remarks published by the airport manager or sponsor through the FAA. Comments are submitted by ForeFlight subscribers and are based on the subscriber’s personal experience at that airport.

FBOs on Taxi Charts
We have received lots of positive feedback on our FBOs on Taxi Charts feature. Fuel seller locations are mapped with an interactive marker right on the taxi chart. Tap on the FBO button in the upper left area of the taxi chart to turn the markers on and off. Tap the marker to see information about the FBO without leaving the chart view.

ForeFlight Directory listing shown on taxi chart

FBOs on Taxi Charts makes FBOs easy to find after the pilot lands. All of the Directory listing details are available right on the taxi chart view.

Questions about ForeFlight Directory? I’d love to hear from you! I’m on frequency at directory@foreflight.com.

ForeFlight Acquires JetFuelX

JetFuelX on any device

We are thrilled to announce this exciting addition to ForeFlight. JetFuelX is a free web-based fuel card management service that makes it easy for owners and operators of turbine aircraft to save money by quickly finding the lowest prices available from their multiple jet fuel discount program memberships.

JetFuelX, A ForeFlight CompanyJetFuelX is designed to help everyone from individual pilots to large flight departments, including charter operators, quickly pinpoint the best jet fuel prices and eliminate the frustrating and time-consuming task of managing and comparing multiple fuel card and FBO discount programs. Customers can manage unlimited fuel card memberships and aircraft profiles, view all prices available at the planned destination, compare prices in real-time with nearby airports, and submit fuel releases in a matter of seconds. The simple search function returns discount pricing information at the planned destination, as well as the nearest airports, in a neatly organized list or interactive map view.

In addition, JetFuelX provides a solution for fuel providers and FBOs to efficiently distribute pricing data to their members. FBOs and fuel providers who are interested in integrating with JetFuelX, please contact info@jetfuelx.com.

Existing JetFuelX customers can continue to enjoy the benefits of this free service. If you are a ForeFlight customer, you can also login with your existing ForeFlight credentials and use the JetFuelX platform at no additional charge. New customers are encouraged to sign up for a free account at www.jetfuelx.com.

Be sure to check out our helpful videos to get you up and running:

 

As always, we are on frequency at team@foreflight.com if you have any questions.

Got Echo Tops?

While not rare, it is a pleasant surprise to see a fairly quiet radar mosaic stretching from coast to coast. Unless you are specifically looking for nasty weather, a tranquil radar usually means decent flying weather, outside of cold clouds, in most locations that are not reporting low ceilings and reduced visibility due to a radiation fog event. This also means you may not see some of the other familiar markers you’d normally expect to be displayed on the Map with the radar layer on. One of these markers that is often missing is the echo top heights.

Benign Radar

Overall, a fairly benign radar with the most significant returns in southern California.

First, let’s get one thing out of the way; echo tops are not the same as cloud tops. Cloud tops are always higher. Second, echo tops represent the mean sea level (MSL) height of the highest radar echo of 18 dBZ or greater. Third, echo tops heights are added to the NEXRAD mosaic in ForeFlight only when the echo tops consistently exceed 20,000 feet MSL. In other words, you won’t see an echo tops report of 15,000 feet, for example. So it’s understandable for customers to believe echo tops may be “missing” from the radar mosaic when the radar is fairly benign. Moreover, there may be some intense-looking echoes in various locations, even some with storm tracks and mesoscale circulations shown, but no echo top heights anywhere to be found. Let’s take a look at a recent example.

In the image above, notice that most of the U.S. is enjoying an early evening free of any significant weather. A few light echoes in southeast Arizona, some light snow in Montana and Idaho, showery precipitation in western Washington and probably the most intense area of weather in southern California. Zooming in on that area below, there are some areas with reflectivity values greater than 40 dBZ (yellow and orange) indicating moderate precipitation. But there’s not a single echo top height displayed even though there are several storm tracks identified. The storm tracks are there since the cellular structure and the relative high reflectivity of the echoes has triggered the NEXRAD algorithms to generate one. However, this algorithm is completely independent of the echo top height.

Southern-CA

Cellular returns indicate showery precipitation. A few cells have storm tracks defined, but despite their intensity, no echo tops are shown.

Despite the intensity of these cells in southern California, the echo top heights are likely below 20,000 feet. Since cloud tops are higher than echo tops, let’s examine the cloud top height in this area. The best way to determine the height of cloud tops is to examine the satellite imagery in ForeFlight like the color-enhanced infrared satellite image shown below. This satellite image shows the cloud top temperature. Notice the pale green colors within the black circle where the most significant returns are located. Using the color bar at the top of the image, these solid pale green colors equate to a cloud top temperature of about -20 degrees Celsius.

IR-Image

The color-enhanced infrared satellite image shows the temperature of the surface of the earth or temperature of the cloud tops. In this case, clouds in southern California have cloud top temperatures of -20 degrees Celsius.

Once the cloud top temperatures are known, it’s a simple process to compare this cloud top temperature against the temperatures aloft using ForeFlight. Below are the Winds and Temperatures aloft for Bakersfield near one of the more intense cells at this same time. This clearly shows at 18,000 feet MSL the temperatures were -6 degrees Fahrenheit or -21 degrees Celsius. So cloud tops in this region were definitely below 20,000 feet.

Temperature Aloft

The ForeFlight Winds and Temperatures aloft show a temperature of -6 degrees Fahrenheit (-21 degrees Celsius) at 18,000 feet MSL over Bakersfield.

If you were paying close attention to the radar loop, you may have noticed that one lone echo top height marker appears (pointed to by the red arrow below) of 201 indicating an echo top height of 20,100 feet in this cell. So when you see a lack of echo tops reported, it just may be that those tops are below 20,000 feet.

One Lone Echo Top

A single echo top height of 20,100 feet MSL did pop up on the radar loop bolstering the idea that most echo tops were below 20,000 feet.

Getting Into The Forecaster’s Head

With ForeFlight 7.5 you’ll have the ability to peer into the minds of forecasters. Yeah, I know… scary thought! No, we haven’t developed a method for mental telepathy within the app; but, we now provide access to the forecaster’s thinking about the latest set of Terminal Aerodrome Forecasts (TAFs) they recently issued. These are referred to as Area Forecast Discussions or AFDs. Let’s take a look at how these can be used in your routine flight planning.

Let’s say you are planning to fly into Charlotte Douglas International Airport (KCLT) arriving in the early afternoon around 1800 UTC and the latest terminal forecast issued at 1140 UTC shows good visibility (P6SM) with showers in the vicinity (VCSH) and a broken ceiling at 7,000 feet (BKN070) at the time of your proposed arrival. Does this worry you even a little bit? After all, high-base rain showers in the vicinity of the airport appears to be fairly harmless even for a pilot flying VFR? Actually, this should concern you – this may just be a forecast for thunder.

CLT-Terminal-Area

The red circle annotated here on the Charlotte TAC represents the 5 statute mile radius of the Charlotte Douglas Airport (KCLT) terminal area. This is the tiny region that forecasters consider when issuing a Terminal Aerodrome Forecast (TAF).

Just because you don’t see a forecast for TS, TSRA or VCTS in a TAF, doesn’t that mean you won’t see thunderstorms arriving or departing that airport. What it could mean is that the forecaster wasn’t confident enough at the time he/she issued the forecast that a thunderstorm would develop within or roll through the region referred to as the terminal area. The terminal area is the region of airspace within a 5 statute mile radius from the center of the airport’s runway complex like the one shown above for the Charlotte Douglas International Airport (KCLT). So it is common for meteorologists to use showers in the vicinity (VCSH) or rain showers (SHRA) as a placeholder for thunder when forecaster confidence is low.

Here’s the problem

The forecaster doesn’t have an obvious way to quantify his/her uncertainty in the actual body of the coded TAF. Quantifying uncertainty is paramount when constructing any forecast (especially one for thunderstorms) and is usually done with a probabilistic approach – you know, a chance of this or a chance of that.

What about the PROB group that you may have seen in a TAF? Sure, that would work, but NWS directives state that a PROB30 group can’t appear within the first nine hours of the terminal forecast. By the way, the NWS only uses PROB30 groups; although you may see PROB40 in TAFs when flying to other countries. So back to the issue – how does a pilot know that showers in the vicinity is a placeholder for thunder in the TAF issued for Charlotte Douglas International Airport?

AFDs to the rescue

First, AFD doesn’t stand for Airport/Facility Directory as you may have thought. It’s called an Area Forecast Discussion. Second, it’s not a discussion about the aviation Area Forecast (FA) issued by meteorologists at the Aviation Weather Center. Are you thoroughly confused yet? The AFD is one of the most commonly accessed products on NWS Web sites, however, very few pilots have even heard of them. Now they are available for you to read beginning to end in the ForeFlight Mobile app!

County Warning Areas

A map of the County Warning Areas (CWAs) across the United States. There is an Area Forecast Discussion (AFD) generated for each one of these CWAs.

The AFD is a discussion that is written by the same forecasters that issue the TAFs. Every NWS local Weather Forecast Office (WFO) throughout the United States issues terminal forecasts for airports that appear within their County Warning Area (CWA), hence the term Area Forecast Discussion. After TAF issuance, meteorologists are required to update the AFD with a plain english discussion explaining their thoughts behind the forecast which allows them a plethora of ways to quantify their uncertainty. AFDs were originally designed as technical discussions to enhance collaboration among NWS forecast offices and to convey uncertainty to a specialized audience. So the language can be quite technical at times, but still highly useful to pilots. Let’s get back to your flight into Charlotte.

The GSP AFD has some clues

For example, the AFD associated with this TAF for the Charlotte Douglas Airport is written by a forecaster located at the Greenville-Spartanburg WFO (GSP) in Greer, South Carolina. Here’s the pertinent part of the discussion that morning:

AVIATION /16Z TUESDAY THROUGH SATURDAY/…

AT KCLT…LITTLE CHANGE FROM 06 UTC PACKAGE AS A WEST WIND LESS THAN 8 KTS UNDER MOSTLY CLEAR SKIES WILL CONTINUE THROUGH MID-MORNING. EXPECT INCREASING WSW WINDS WITH LOW AMPLITUDE GUST POTENTIAL BY MIDDAY AND PERHAPS PERIODS OF VFR CEILINGS THROUGH THE AFTERNOON. SCATTERED SHOWERS AND A PERHAPS A THUNDERSTORM…ARE EXPECTED ACROSS THE NORTH CAROLINA PIEDMONT FROM THE AFTERNOON UNTIL EARLY EVENING AND WILL CARRY VCSH FOR NOW TO COVER THAT THREAT. DEEP CONVECTIVE ACTIVITY WILL DIMINISH BY MID-EVENING WHEN A WIND SHIFT TO NORTHWEST IS EXPECTED.

As stated in this AFD text that is highlighted above, the forecaster opted to use showers in the vicinity (VCSH) to cover the threat for thunder in the North Carolina Piedmont region where KCLT is located. Most pilots don’t realize or appreciate that showery precipitation is actually a convective process. So forecasters will often use showers as a placeholder when confidence of thunder is low. This is not to say that every forecast for showers is used in this way, but that is a common way the forecaster quantifies his/her uncertainty for convective events such as this.

For whatever reason, the forecaster wasn’t quite confident enough to impart a little meteorological risk and add thunderstorms to the Charlotte TAF. This is in part due to the relatively small size of the terminal area. If the thunderstorms in the area are anticipated to be of a scattered nature (as it was on this day), they will often omit a forecast for thunder until they are more certain thunderstorms will indeed impact the terminal area. In some situations they may use showers to hint that convection will be in the area without adding TSRA or VCTS to the forecast. As the convective weather event evolves and certainty increases, they will issue an amended forecast to add thunder. But these details are not part of the official forecast. For better or for worse, they are buried in the AFD. The AFD is the place where the forecaster can freely quantify his/her uncertainty and provide some background on why the forecast is constructed the way it is.

Moreover, meteorologists at the local weather forecast offices that issue forecasts for high impact terminal areas such as Charlotte Douglas have a fair amount of outside pressure from the airlines to avoid adding thunder to the forecast unless convection is fairly certain. A forecast for thunder at the proposed time of arrival means the airlines must file an alternate and carry extra fuel to get to that alternate.

So what actually occurred at Charlotte Douglas?

Did thunder ever affect the Charlotte terminal area? Yes, at 1813 UTC the observation (METAR) included a report for a thunderstorm at the airport as shown below.

KCLT 271813Z 07003KT 10SM TS SCT040CB BKN090 BKN200 16/09 A2956
RMK AO2 TSB13 OCNL LTGIC TS SE-SW-W MOVG E CB NW-N MOVG E

But, it wasn’t until 1739 UTC (a mere 34 minutes earlier) that the forecaster amended the TAF to include a forecast for light rain and thunder as shown below.  Some pilots might opine that the TAF issued at 1140 UTC was a bad forecast. However, given the scattered nature of the convection on this day (read uncertainty) the placeholder of showers in the vicinity was the method used to indicate the risk of thunder. The AFD was the place the forecaster documented this important piece of information.

KCLT 271739Z 2718/2818 26008G18KT 6SM -TSRA BR BKN045 OVC070CB
TEMPO 2718/2720 25010G20KT 5SM -TSRA BR SCT030 OVC050CB…

The AFD format

The raw AFD doesn’t have a rigid syntactical or semantic format that forecasters must follow. Moreover, that format may differ from one forecast office to the next. That’s both good and bad. At ForeFlight we do make an attempt to visually separate the discussion into sections with a header where it is possible. Although you may find that some WFOs do a better job than others sticking to a common format as described below; so don’t count on perfection with the AFDs.

AFD Synopsis

Most Area Forecast Discussions (AFDs) will contain a synopsis section followed by a near-, short-, and long-term discussion. Simply scroll the window down with your finger or stylus to see the rest.

Each AFD will typically start out with a SYNOPSIS section (as shown above) followed by a NEAR TERM, SHORT TERM and LONG TERM discussion. This is the accepted format for the NWS Eastern Region. In other regions you may just see one big DISCUSSION section. While not specific to aviation, these sections are important to read and often may describe the “big picture” and point out many clues and trends as to what adverse weather might occur over the next several hours or even several days. Of the most interest to pilots, every AFD will also include an AVIATION section like the one shown below. This is the section where the forecaster discusses the TAFs and aviation-specific concerns. Lastly, in some parts of the country you may find a separate section that discusses fire dangers and marine weather.

AFD Aviation

Every AFD should have an aviation section. The AFD is automatically scrolled to this section when first viewed. Also notice that key words or phrases may be highlighted in red to point out the discussion of various adverse weather elements.

While most of the sections in the AFD are word-wrapped, you may see some tabular sections like the confidence table shown below. In order to preserve the columnar format within this section, you can scroll these sections left and right with your finger or stylus (notice the horizontal scroll bar below this table).

AFD Tabular

Some sections in the Area Forecast Discussion (AFD) are tabular. In these cases, the section can be scrolled to the right to see the remaining part of the table.

Finding the AFD in ForeFlight

The AFD is available to all ForeFlight subscribers and to locate it in the app is as simple as finding a METAR or TAF. On the Map, bring up any airport-specific layer such as Flight Category and tap on the airport marker. Next, tap the Forecast tab at the bottom of the pop-over window then tap on the new Discussion button at the top to reveal the AFD for that airport’s CWA as shown below. The Discussion button will be located to the right of the MOS button.

AFD Location

The Area Forecast Discussion (AFD) is located under the Forecast tab on the station popover right next to the MOS button.

You can also view AFDs in the Airports view. With the airport of interest displayed, tap on the Weather tab, then tap on Forecast Discussion as shown below. However, be careful not to confuse this with the Airport/Facility Directory (A/FD) tab.

AFD Airports view

The Area Forecast Discussion (AFD) can be shown within the Airports view similar to the way METARs, TAFs and MOS are displayed.

The Fine Print

When tapping on the Discussion button in the pop-over window, the AFD is auto-scrolled to the Aviation section. From there you can scroll up or down to read the rest of the forecast discussion. Similarly in the Airports view, the Aviation section is also displayed first by tapping on Forecast Discussion under the Weather tab. Tapping on Forecast Discussion again, will position it to the beginning of the discussion text.

While most of the discussion is in plain english, there will be times where abbreviations and acronyms will rear their ugly head. We’ve made an honest attempt to decode most (but not all) of these within the text. Moreover, you will see some words and phrases highlighted in red. Hopefully these will grab your attention since they sometimes point out discussion that includes more extreme adverse weather.

Mind the limitations

AFDs are only available for airports within the United States (including Hawaii and Alaska). So selecting any airport within the U.S. should result in retrieving the latest AFD based on the CWA that airport is located within. Consequently, airports outside of the U.S. won’t have a Discussion button on the pop-over or under the weather tab on the Airports view. Occasionally, the latest AFD may not be available and you’ll see a “No forecast discussion” response. This is a very rare occurrence, but it may happen from time to time.

While some forecasters put a fair amount of time and detail describing their thoughts, not all AFDs will have details you might be hoping to learn. The AFD isn’t their highest priority; when the weather is busy the AFDs will often get the short end of the stick. That same forecaster may have to help with radar and issuing severe thunderstorm and tornado warnings on a busy convective day, for example.

In the end, expect the AFDs to provide a complementary product to the TAFs. If you are not reading the AFDs, you are only getting half the story.

ForeFlight Web Moves to Open Beta

ForeFlight Web is now in open Beta, meaning that anyone with an active ForeFlight subscription can access it. Just go to plan.foreflight.com and sign in using your ForeFlight username and password.

ForeFlight Web

Plan a flight or view weather and airport information all from your web browser. Routes are synced to ForeFlight Mobile on all your devices, allowing you to pick up at the airport right where you left off at home.

As a Beta program, we’re continually refining and adding new features to ForeFlight Web, and we welcome any feedback you have about how it can be improved.

Learn more at foreflight.com/web.

Weather On The Front Lines

If you surveyed a group of general aviation pilots, it would probably not surprise you to learn that Center Weather Advisories are not a weather source that pilots use very frequently when planning a flight. They have always been included within the ForeFlight Mobile app by tapping the Brief button under File & Brief. But this standard briefing only provides the advisory in raw text form—unless of course you are using the new and improved ForeFlight Briefing where it is also displayed graphically. In ForeFlight Mobile 7.4, Center Weather Advisories are now depicted graphically within the existing AIR/SIGMET layer on the Map view making them even more useful.

In-flight advisory

Center Weather Advisories, or CWAs, are the “front lines” of aviation weather in the U.S. for adverse weather such as low IFR conditions, thunderstorms, icing, and turbulence. While they smell a lot like AIRMETs and SIGMETs, they are more of an in-flight advisory about current conditions than they are a planning tool or forecast. Therefore, it’s critical to look for these while en route to your destination and just before you close the door to depart. Now is a good time to mention that CWAs are not part of the ADS-B broadcast so you will not receive them while connected to a Stratus.

Center centric

CWAs are issued by highly trained meteorologists at the Center Weather Service Units (CWSUs) located at the various Air Route Traffic Control Centers (ARTCCs) pictured below.

ARTCC Map

A map of the Air Route Traffic Control Center (ARTCC) boundaries in the U.S. Each ARTCC has a Center Weather Service Unit (CWSU) staffed by meteorologists that are responsible for issuing Center Weather Advisories (CWAs) for their respective ARTCC area.

CWAs are issued to warn pilots of the following in-flight weather hazards:

  • Conditions meeting or expecting to meet convective SIGMET criteria
  • Moderate or greater airframe icing
  • Moderate or greater turbulence
  • Heavy precipitation
  • Freezing precipitation
  • Conditions at or approaching Low IFR
  • Sustained surface winds/gusts > 30 knots
  • Non-convective low level wind shear below 2,000 feet AGL
  • Volcanic ash, dust storms, or sandstorms

Short lead time

Unlike their AIRMET counterpart, CWAs are not routinely issued and have no defined schedule. Moreover, they have a very short lead time since they are issued on an as-needed basis. So it’s not unusual to see a CWA issued at 20 minutes past the hour to describe adverse weather that has evolved very rapidly. Once issued, CWAs are valid for two hours or less. If conditions are anticipated to persist beyond two hours, it will be indicated in the last line of the CWA text. As mentioned earlier, CWAs are not as valuable of a preflight planning tool because of its short lead time and duration. They tend to pop up as adverse weather evolves or develops throughout the U.S. and along its coastal waters.

Complementary guidance to other advisories

Forecasters at the CWSUs have a fair amount of latitude when issuing a CWA. Conditions do not have to meet national in-flight advisory criteria in terms of intensity or areal coverage. For example, unlike convective SIGMETs, CWAs for convection can be issued before thunderstorms have formed. That is, they can describe a broad area of towering cumulus or showery precipitation that is trending toward an aviation hazard within the next two hours especially in regions that may affect flow into or out of busy airspace. Convective SIGMETs issued by forecasters at the Aviation Weather Center (AWC) are more of a NOWcast that warn pilots about active areas of thunderstorms that have already met specific hazard criteria.

A good example of its complementary nature is a CWA for low IFR conditions. An AIRMET for IFR conditions is primarily directed at pilots flying under visual flight rules (VFR). It describes an area that may experience a ceiling and/or visibility below VFR minimums. However, what if a portion of the AIRMET region is also plagued with persistent low IFR conditions? This would be critical information for all pilots including those flying under instrument flight rules (IFR). As shown below, given the number of stations reporting low IFR conditions (magenta markers) within the AIRMET region, the Denver CWSU issued a CWA for ceilings at or below 500 feet and visibility at or below 1/2 statute miles.

Low IFR CWA

This Center Weather Advisory (CWA) was issued for ceilings at or below 500 feet and visibilities at or below 1/2 statute mile that were occurring within an existing AIRMET for IFR conditions.

While CWAs can be issued at any time, they are generally coordinated with other agencies within NOAA to ensure meteorological consistency between products. This includes meteorologists at the AWC who are responsible for issuing the area forecast, AIRMETs, SIGMETs and convective SIGMETs. It’s pretty typical for the meteorologist at the CWSU to have a brief phone conversation with the appropriate meteorologist at the AWC before issuing a new CWA.

Finding CWAs in ForeFlight

The CWA layer can be displayed from the Map view in ForeFlight Mobile 7.4. Simply tap the Map mode button in the upper left and select AIR/SIGMET/CWAs from the menu as shown below:

CWA Menu

Center Weather Advisories (CWAs) can be selected from tapping the mode button and selecting AIR/SIGMET/CWAs from that menu.

Once the layer has been selected you will see CWAs depicted on the ForeFlight map view as cyan-colored polygons regardless of the hazard type. In most cases, these areas will be smaller in size than an AIRMET or SIGMET because of their complementary nature and short duration. To see the associated uncoded text of the CWA, simply tap on the polygon in the same way that you view the uncoded text for AIRMETs and SIGMETs. Be sure to always read the text of the CWA since it will have additional details about the flight conditions such as the altitudes affected and an indication of whether or not conditions are expected to improve or persist beyond the valid time.

Buttons

When AIR/SIGMET/CWAs are selected, the four buttons at the bottom of the Map allow you to filter advisories according to hazard type.

Lastly, given that CWAs are a complementary product to AIRMETs, SIGMETs and convective SIGMETs, with ForeFlight Mobile 7.4 you can overlay them with other advisories. Tapping on the buttons at the bottom labeled Ice, Turb, IFR and TS, will permit you to add or remove CWAs from the Map based on hazard type. In this example above, only IFR hazards are selected which includes AIRMETs for IFR conditions and mountain obscuration as well as a single CWA for low IFR conditions captured by the cyan-colored polygon. Any advisories for icing, turbulence and convection (if any) have been filtered from the Map.

More Turbulence Is Better

No, we’re not gluttons for punishment; however, the turbulence Imagery in ForeFlight Mobile has just gotten way better! Forecasts now go out beyond 12 hours to include lead times of 15 and 18 hours. This is a significant improvement to NOAA’s Graphical Turbulence Guidance (GTG-3) product that now includes an analysis and forecast for clear air turbulence as well as turbulence from mountain wave activity with a new forecast updated every hour. Whereas the lowest altitude in the earlier version of GTG originated at 10,000 feet, the new GTG product includes low-level turbulence beginning at 1,000 feet MSL with a vertical resolution of 2,000 feet that extends to FL450. If that isn’t enough, forecasts now have a higher resolution of turbulence intensities that includes the full range of classifications from light to extreme as shown below making the product even more useful to evaluate the risk of dangerous turbulence along your proposed route.

Eddy Dissipation Rate (EDR)

Turbulence intensities now include light (blue to green), moderate (green to orange), severe (orange to red) and extreme (red to dark red).

Eddy Dissipation Rate (EDR)

On the older GTG version, the legacy terminology such as light or moderate turbulence is somewhat arbitrary and based typically on the response of the aircraft to the turbulence, not the atmospheric conditions themselves. Shown in the scale above, Eddy Dissipation Rate, or EDR, is an objective, aircraft-independent, universal measure of turbulence based on the rate at which energy dissipates in the atmosphere. In other words, it is a measure of the turbulent state of the atmosphere. According to turbulence researcher, Dr. Robert Sharman, “When the atmosphere is dissipating energy quickly (i.e the EDR is large), atmospheric turbulence levels are high.” Pilots should be keenly aware that a safe turbulence penetration airspeed varies with the aircraft’s weight which Dr. Sharman quickly points out, “The implication for aircraft bumpiness depends on the size (weight) of the aircraft.”

At the basic level EDR is really an in situ calculation. That is, it is a value determined by an aircraft while in flight. However, it is not directly measured by the aircraft like outside air temperature, for example. Instead it’s determined by using a variety of data from aircraft avionics which means aircraft can (and do) automatically report EDR in flight. Since EDR is an aircraft-independent calculation, a single engine Cessna 152 and a Boeing 747 should determine the same EDR value when flying through the same atmosphere at the same time.

It’s one thing to calculate the EDR in flight, but totally another challenge to provide a forecast for this field. That’s the job of GTG-3. Dr. Sharman points out, “From the forecasting point-of-view we cannot provide a separate forecast for every type of aircraft that is out there.” So depending on the class of aircraft you are flying, there’s a need to evaluate the EDR values properly. Below shows the EDR values that correspond to light-, medium- and heavy-weighted aircraft as they loosely relate to the vertical acceleration/deceleration (turbulence) response in that class of aircraft.

EDR Light

Eddy Dissipation Rate (EDR) scale for light-weight aircraft.

EDR Medium

Eddy Dissipation Rate (EDR) scale for medium-weight aircraft.

EDRHeavy

Eddy Dissipation Rate (EDR) scale for heavy-weight aircraft.

The new version of GTG includes a forecast for clear-air turbulence often referred to as CAT. Even more exciting, turbulence that is a direct result of mountain wave activity, or MTW, is also forecast separately. While these forecasts are not meant to predict turbulence associated with deep, moist convection, they will provide guidance of low-level terrain and thermally-induced turbulence sources.

To that end, in the ForeFlight Imagery view you’ll find three different forecasts that include clear-air turbulence (CAT), mountain wave turbulence (MTW) and one that combines the two (All). Each one of these is organized into low (1,000 ft – 13,000 ft), middle (15,000 ft -FL290) and high (FL310 – FL450) level collections as shown below.

Turbulence Selections

Turbulence forecasts in the ForeFlight Mobile Imagery view are organized by clear air turbulence (CAT), mountain wave turbulence (MTW), and forecasts that combine the two (All). Each type provides low, medium and high altitude collections beginning at 1,000 ft MSL up to and including FL450.

The GTG forecasts have been approved by the FAA for unrestricted use for preflight planning as stated below on the Aviation Weather Center website:

“GTG is generated operationally at NOAA/NCEP which is supported 24 hours a day, 7 days a week. Its use is unrestricted (meteorologists, dispatchers, GA and commercial pilots, ATC, etc).”

Keep in mind that these are automated forecasts and do not have any human input like you might find with AIRMET Tango, SIGMETs for severe or extreme turbulence and Center Weather Advisories (CWAs). When used in combination with these forecaster-generated products and pilot weather reports, GTG will provide you with the ability to minimize your exposure to dangerous turbulence and find the altitude with smoothest ride.

Decoding Wind Shear

It’s early in the morning and you’re preparing to depart on an IFR flight out of Asheville (KAVL) in western North Carolina. While finishing your breakfast you open up the ForeFlight Mobile app, insert your favorite route to your destination and tap the little suitcase to pack all of the current charts, NOTAMs, fuel prices and latest weather for your flight. While ForeFlight is packing everything that you need (love that feature!), you decide to take a peek at the latest terminal forecast for Asheville (below) and see something that doesn’t look too appealing – WS020/07040KT; ForeFlight translates this initial part of the TAF to a forecast for wind shear. Ugh!

Wind shear forecast for Asheville

A terminal forecast for non-convective low-level wind shear (LLWS) as shown in ForeFlight.

So you tap on the Imagery tab and select the Graphical AIRMETs collection and see under Tango a forecast for low-level wind shear (LLWS) covering a large area from the panhandle of Maryland southwest to northern Georgia as shown below. This area impacts a good portion of your proposed route including your departure out of Asheville. Now what? Cancel the flight since you don’t want to be fooling around with wind shear in the mountains? Perhaps, but let’s take a closer look at this particular forecast and what it really means.

us_LLWS_2

A forecast for non-convective low-level wind shear (LLWS) issued by the Aviation Weather Center in the form of a Graphical AIRMET (G-AIRMET). The actual magnitude of the wind shear or direction is not provided in the G-AIRMET.

Both of these forecasts identify the potential for non-convective low-level wind shear (LLWS). This is perhaps the most misunderstood weather forecasts in aviation. Pilots hear the term wind shear and immediately equate this to severe turbulence. It is not a forecast for turbulence per se and is definitely not the same wind shear you might experience in and around areas of convection since it has nothing to do with thunderstorms. So now that we know what it is not, let’s dig a bit deeper.

Define, please?

Wind shear is defined as a marked change of wind speed and/or wind direction over a horizontal plane or within a vertical depth of the atmosphere. When the wind shear occurs near the surface, it is referred to as low-level wind shear and abbreviated LLWS. Non-convective LLWS as it appears in a TAF or within AIRMET Tango (also G-AIRMETs) is primarily a form of vertical speed shear. That is, the wind is forecast to rapidly increase with height within the wind shear layer. In addition, winds may also change direction with increasing altitude within the wind shear layer – although it is primarily a forecast for a change in wind speed.

Decode, please?

Here’s the pertinent part of the coded Asheville TAF shown above:

01008KT 6SM -SHRA BR OVC015 WS020/07040KT

Decoded, this TAF suggests that between 1200 and 1600 UTC the surface winds will be 010 degrees (true) at 8 knots with a visibility of 6 statute miles with light rain showers and mist and an overcast ceiling of 1,500 feet. Easy so far? Now the confusing part. The WS code following all of this translates to non-convective low-level wind shear. The 020 following the WS code defines the depth of the wind shear layer which is 2,000 feet above ground level (AGL) in this case. Two thousand feet is the maximum depth forecast, but you may also see 005 (500 feet), 010 (1,000 ft) or 015 (1,500 ft). But it’s also acceptable to see 018 representing an 1,800 ft depth to the wind shear layer.

The remainder of the code following the forward slash defines the wind speed and direction at the top of the wind shear layer. Therefore, 07040KT translates to a wind direction of 070 degrees (true) at 40 knots at 2,000 feet AGL. Putting it all together, the winds are expected to increase rapidly from 8 knots at the surface to 40 knots at 2,000 feet AGL. This forecast also implies that winds will also shift direction from 010 degrees at the surface to 070 degrees at 2,000 feet although there’s no way to know how or where the shift occurs within the wind shear layer. Now that you are an expert decoder of the wind shear forecast in a TAF, what does it mean to you as a pilot?

Meaning, please?

As mentioned earlier, this is not a forecast for severe turbulence as many pilots might have been taught. Forecast or not, it is a common phenomenon and you may have flown through it and did not even know it was there. In fact, in the evening and overnight hours a nocturnal temperature inversion is often the catalyst for non-convective LLWS to evolve. In the nocturnal flavor of non-convective LLWS, the sky is often clear and the winds at the surface are usually light or calm. But the air in the wind shear layer remains glassy smooth. The only thing you may notice is a change of groundspeed as you penetrate the layer.

Essentially, non-convective LLWS is a river of faster flowing air just above the surface whether it occurs during the day or night. More often than not, a surface-based temperature inversion is present and as mentioned above is the primary catalyst for this form of wind shear. Normally the temperature decreases with increasing altitude. However, with an inversion the temperature actually increases with height through some depth. Meteorologists call this a negative lapse rate. The more negative the lapse rate, the more stable the atmosphere. A stable atmosphere resists or inhibits upward or downward motion keeping the potential wind shear layer near the surface from mixing. No mixing yields no turbulence.

ILS7

Profile view from the ILS approach to runway 7 at Rockford, Illinois.

Beware on approach

Even though the air may be glassy smooth, imagine the case where you are flying an instrument approach with this kind of wind shear in place. Even if the wind doesn’t change direction in the wind shear layer, you will still have to contend with the change of wind speed that is increasing rapidly with height from the surface. If the wind is right off your nose and you are flying an ILS, for example, you will notice as you intercept the localizer around 2,000 ft AGL your groundspeed will be abnormally low (you have a 40 knot headwind in the case for Asheville). As you begin to track the glideslope, your groundspeed will increase since the headwind is decreasing in the descent. This means you’ll have to increase your rate of descent to keep the glideslope needle centered.

You can also imagine this being a tailwind or a direct crosswind while on the approach. So you have be constantly changing the descent rate or heading (crab angle) into the wind. Keep in mind that non-convective LLWS comes in all shapes and sizes. There’s not a one size fits all method to handle this. In most cases, this form of wind shear is not something you should fear, but it’s something you definitely need to manage. It is probably present more than it’s forecast.

Stay tuned

Besides the shear in the overnight hours discussed above, non-convective LLWS may be associated with the following: frontal passage, lee side mountain effect, sea breeze front and Santa Ana winds just to name a few. In a future blog I will discuss the meteorology behind non-convective LLWS and provide some background when this phenomenon can become dangerous.